Succession Notes. Example of succession: 1) Primary Succession: What is ecological succession? Why does an ecosystem change?

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1 Succession Notes 1 Topic: Succession What is ecological succession? The process where plants & animals of a particular area are replaced by different more complex species over time. The natural aging of the ecosystem. Reflects the ongoing struggle by different species for enough light, nutrients, food, water, and space (abiotic & biotic factors). 2 Example of succession: 3 Why does an ecosystem change? The species types & numbers change in response to changing environmental conditions such as fires, climate change, & the clearing of forests to plant crops. As years pass, organisms (plants, animals, bacteria, protists, or fungi) change the environment in which they live. 4 Ecologists recognize 2 types of succession: The new environment is no longer a suitable habitat for the organisms that first lived there. New species enter the ecosystem and crowd out the original inhabitants. 1) Primary succession 2) Secondary succession 5 1) Primary Succession: Involves the gradual establishment of biotic communities in lifeless areas where there is no soil in a terrestrial ecosystem or no bottom sediment in an aquatic ecosystem. Ex: bare rock exposed by a retreating glacier or severe soil erosion, newly cooled lava from a volcanic eruptions, an abandoned highway or parking lot, & a newly created pond or reservoir. 6

2 Takes a long time. There s no fertile soil to provide nutrients needed to establish plant growth. Bare rock weathers by crumbling into particles & releasing nutrients. a) Physical weathering occurs when a rock is fragmented, as water in its cracks freezes & expands. b) Chemical weathering happens when rocks react w/substances in the atmosphere or w/precipitation which can break down the rock s surface material. 7 8 Example of Primary Ecological Succession: Over a thousand years, plant communities developed that had previously started on bare rock exposed by a retreating glacier on Isle Royal, Michigan in northern Lake Superior. Pioneer or Early Successional Species: This is where the slow process of soil formation begins. Ex: lichens and mosses whose seeds or spores are distributed by wind or carried by animals. Exposed rocks Lichens and mosses Small herbs and shrubs Heath mat Jack pine, black spruce, and aspen Balsam fir, paper birch, and white spruce forest community 9 10 lichen - An alga & a fungus interacting in a mutualistic relationship. Fungi provide protection & support for the algae. Algae, through photosynthesis, provides sugar nutrients for both species. 11 Pioneer or Early Successional Species: Trap wind-blown soil particles & tiny pieces of detritus, & add their own wastes and dead bodies to the beginning soil fragments. They also secrete mild acids that further breakdown the rock. As lichens spread, drought-resistant mosses start growing in the cracks, which help form a mat that traps moisture. When lichens & mosses die, their decomposing remains add to the growing layer of nutrients. 12

3 Mid-Successional Plant Species: After hundreds to thousands of years, the soil may be deep & fertile enough to support this type of growth. Ex: herbs, grasses, & low shrubs. As shrubs grow & create shade, the lichens & mosses (pioneer species) die from lack of sunlight. Trees that need lots of sun that are adapted to the area s climate & soil Late-Successional Plant Species: As tree species that need sunlight grow & create shade, they are replaced by this type of plant growth. Ex: shade-tolerant tree species Unless natural or human processes disturb the area, what was once bare rock becomes a complex forest community = climax community. usually replace the grasses & shrubs Climax Communities: Stable area dominated by longlived plant species. 15 2) Secondary Succession: Most common type of succession. A series of communities or ecosystems develop in places containing soil or bottom sediment. Begins in an area where the natural community has been disturbed, removed, or destroyed, but soil or bottom sediments still remain. 16 2) Secondary Succession: Ex: abandoned farmland, burned or cut forests, heavily polluted streams, & land that has been flooded. Within a few weeks new vegetation can germinate from the soil left on disturbed land systems. From seeds already in the soil. From seeds imported by wind, birds, & other animals. 17 Example of Secondary Ecological Succession: It took years after a farm field in NC was abandoned to become covered with a mature oak and hickory forest climax community. A new disturbance, such as deforestation or fire, would create conditions favoring pioneer species such as annual weeds. Annual weeds Perennial weeds and grasses Shrubs and small pine seedlings Young pine forest with developing understory of oak and hickory trees Mature oak and hickory forest 18

4 Examples of Successional Stages: Land (terrestrial): rock lichen, mosses small shrubs large shrubs small trees large trees Examples of Successional Stages: Water (aquatic): bare bottom small/few underwater vegetation temporary pond and prairie forest and swamp Descriptions of succession usually focus on vegetational changes: But these changes also affect food & shelter for various animals. Succession changes numbers & types of animals Primary & secondary succession: Increase biodiversity. Increase sustainability of communities & ecosystems by increasing species richness & interactions among species. Promote population control. Give rise to more complex and decomposers too. food webs Due by the end of our next class! Foldable on the Stages of Succession of a Pond in the Deciduous Forest Biome: Follow directions on handout!!! Refer to Chapter 1.8 (starts on page 36) Six stages of succession: pioneer stage, submerged plant stage, emerging plant stage, marsh, swamp, and beech-maple forest 23 Successional stages of a pond (in the eastern U.S.): 1)Pioneer stage When first formed, a pond has a sandy or muddy bed; bare bottom stage. Mussels, clams, caddisfly larvae, nest-making fish: feed on algae, protozoa, 24 bacteria, crustaceans.

5 In time, organisms form humus: The death & decay of organisms form a layer of organic matter that covers the bottom of the pond and allows larger algae and pond weeds 2)Submerged plant stage Where the plants do not reach the water s surface. Egg-laying fish, dragonfly & mayfly nymphs, new species of mussels and caddisfly larvae found here. to grow )Emerging plant stage As the pond continues to fill in, the thicker layer of humus on the bottom allows larger plants to become rooted where they extend above the surface of the pond. Pioneer species are now gone. Diving spiders & beetles, crayfish, worms, frogs, turtles, salamanders, catfish, 4)Marsh Where does the water in a marsh come from? When there are no longer any areas of open water; only shallow water with grasses and other rooted plants. Frogs, salamanders, crayfish, leeches, turtles, snakes present. Springs, streams, lakes, rainfall, or tides (for saltwater marshes). & leeches present )Swamp As humus builds up, the marsh becomes drier & trees invade the area; this area will be wet, often flooded during the spring and fall. 6)Beechmaple forest As floods deposit soil in the swamp, this area continues to fill in and more trees invade to where the ecosystem eventually reaches the climax community

6 What is the climax community? The final stage in succession that remains until it is disturbed by some natural event such as fire or human activity. 31 Successional stages of a pond on the western plains: 1. Pioneer 2. Submerged plant 3. Emerging plant 4. Marsh 5. Grassland or prairie 32 Why don t trees invade the great plains? Trees are not given a chance to grow because of disturbance: Natural fires: because most of a grassland s plant matter is stored in underground roots, its ecosystems have high resilience & can recover quickly after a fire as their root systems produce new grasses. Farm equipment cultivating What about the areas that are not disturbed? The process of succession will reach the forest stage unless there aren t enough nutrients in the soil or enough rainfall to support the growth of trees. the land There are limits to the stresses that ecosystems & global systems (climate) can take: Such systems can reach a tipping point, where any additional stress can cause the system to change in an abrupt and irreversible way that often involves collapse. 35 Topics, Concepts, Review Ex: once a certain number of trees have been eliminated from a stable tropical rain forest, it can crash & become a grassland instead of reaching a forest community. Nutrients stored in vegetation, not in the soil as in most other terrestrial ecosystems; once nutrient-rich vegetation is gone, daily rains leach out remaining soil nutrients & prevent the forest from re-growing. 36

7 Topics, Concepts, Review Can change an area s climate by decreasing the input of water vapor from its trees into the atmosphere without such water vapor, rain decreases & the local climate gets warmer allowing for development of a tropical grassland instead of the reestablishment of a tropical rain forest. Ex: continuing to warm the atmosphere by burning fossil fuels that emit CO 2 and cutting down tropical forests that help remove CO 2 could eventually change the global climate system in ways that What is one of the most urgent scientific research priorities today? To identify tipping points and to develop strategies to prevent natural systems from collapsing. Exceeding a tipping point is like falling off a cliff: there is no way back. could last for thousands of years Finish your Foldable! IT IS DUE TODAY 39